The present invention relates to a shrinkable polyester film having excellent shrink characteristics. More particularly, relates to a shrinkable polyester film which is free from wrinkle of the film at the time of shrinkage, curling at the end of the film and non-uniform shrink.
Hitherto, shrinkable films made of polyvinyl chloride or polystyrene have been most popularly used in the field of shrinkable films for labels. These films, however, had the problems in combustion at the time of disposal of the films and recovery of the films from polyethylene terephthalate (PET) bottles. Recently, attention is focused on polyester shrinkable films for their potentialities in solving these problems.
These conventional polyester shrinkable films, however, were generally poor in shrink characteristics as they tended to be wrinkled or curled at the end thereof after shrinkage or would have non-uniformity in the degree of shrinkage. Therefore, the printed labels using such polyester shrinkable films involved problems such as non-uniformity in shade of prints after shrinkage and are not suitable for practical availability.
The present inventors had previously proposed a polyester shrinkable film improved in shrink characteristics in Japanese Patent Application Laid-Open (KOKAI) No. 110931 (1989).
The improvements proposed in the prior application, however, were not always satisfactory. For example, when this film was shrunk at a high temperature and in a short time as in case of labelling a heat-resistant PET bottle or glass bottle, there could occur wrinkle of the label, curling at the end, non uniform slide of prints, etc., making the film impractical for such use. Especially in labelling of heat-resistant PET bottles, it has been tried to reduce the time for shrinking work to meet a rapid increase of demand for PET bottle in recent years, but it was very difficult to use the conventional polyester shrinkable films under such conditions.
Thus, it has been an urgent request in the industry to develop a shrinkable polyester film which is free of the above problems in disposal and recovery and also greatly improved in shrink characteristics.
In view of the above, the present inventors have made further studies on the subject matter and found that a shrinkable polyester film having certain specific properties shows very excellent shrink characteristics in use as a shrink film for labels. The present invention was attained on the basis of such a finding.